Delay:

Chorus / Phaser / Flanger:

Manipulates the sound by duplicating the source sound and summing with subtle pitch modulation. My favorite plugin for chorus effect is TAL-Chorus-LX

Panning:

Changes the volume of left and right signal of the sound

Haas Effect:

Makes the sound wider by changing the time offset between left and right signal

Double Tracking:

Recording the same instrument twice and then panning one to left and second to right.

For me, Reverb is the best approach to make any sound wider.

Why?

Reverb gives the sound a space and depth and makes you hear the sound in more natural way. Remember, you don’t make the sound natural. You make the listener perceive the sound in natural way psycho-acoustically.

In this video, I have shown the right approaches to make your stereo mix sound wider.